Exchange Reaction and Crystallization in Blends of Liquid Crystalline Copolyester and Polycarbonate or Polyamide 6
|關鍵字:||雜式液晶共聚酯;相容性;酯交換反應;晶型轉變;酯-胺交換反應;random copolyester;miscibility;transesterification;crystal form trasformation;ester-amide exchamge|
由P46/PC摻合物的酯交換反應動力學之研究，我們發現在P46中的POB段與PC形成bisphenol A-oxybenzoate dyad酯交換反應的活化能為在P46中的PET段與PC形成bisphenol A-terephthalate dyad酯交換反應活化能的2倍(94.6與41.8 kcal/mol)。這是由於oxybenzoate與oxybenzoate間之化學鍵比ethylene與terephthalate間之化學鍵較為穩定之故。此外，由於P46中含有硬棒(rigid-rod)結構的POB段，因此POB段與PC的酯交換反應之pre-exponential factor會大於PET段與PC的pre-exponential factor (1036與1014 min-1)。
第二部份為研究莫爾分率為60/40的雜式液晶共聚酯POB-PET(簡稱為P64)與聚醯胺(polyamide 6，簡稱為PA6) 摻合物的相容性、結晶性與酯-胺交換反應。雖然P64與PA6的Tg點相近( 60.9℃與50.4℃)，但是由隨組成改變的單一Tg點以及從熔點下降分析獲得的Flory-Huggins作用參數為－0.18，我們可以得知P64與PA6為部份相容。當PA6中含小量的P64，大約為5%，會使得急速冷卻的PA6產生alpha-form結晶。再者，5/95 P64/PA6摻合物的gamma->alpha晶型轉變的起始溫度比純PA6的gamma->alpha晶型轉變的起始溫度降低30℃ (160℃與130℃)。
利用13C 核磁共振光譜儀研究雜式液晶共聚酯P64與聚醯胺(PA6)的摻合物之酯-胺交換反應動力學。我們可以發現在260℃持溫15分鐘即有酯-胺交換反應發生。特別的是，在30/70、50/50與70/30 P64/PA6 摻合物中的酯-胺交換反應活化能幾乎相同，大約為24.0 kcal/mol。而30/70與70/30 P64/ PA6摻合物的pre-exponential factor分別為2.01×1011 min-1與2.74×1012 min-1；另外50/50 P64/PA6摻合物有最低的pre-exponential factor為2.59×1010 min-1。在P64/PA6摻合物中不同的pre-exponential factor可以解釋為與摻合物的相容性有關。|
Miscibility in blends of random liquid crystalline copoly(oxy- benzoate-ethylene terephthalate) at molar ratio 40/60 (P46) and polycarbonate (PC) were investigated with differential scanning calorimetry and polarized optical microscopy. The originally immiscible blend of P46 and PC, displaying two distinctive glass transition temperatures, became partially miscible after annealing at 250oC for 30 min as evidenced by the approaching of the two glass transition temperatures in the differential scanning calorimetry measurement, accompanied with a large loss of the liquid crystalline phase in the polarized optical microscopy study. The kinetics of transesterification in blends of P46 and polycarbonate at melt state were analyzed quantitatively with 13C nuclear magnetic resonance, and were then modelled by a phenomenological equation. It was found that the activation energy for the interchange reaction between the poly(oxybenzoate) segment and polycarbonate was more than twice of that for the interchange reaction between the poly(ethylene terephthalate) segment and polycarbonate (i.e. 94.6 versus 41.8 kcal/mol). This is probably due to the stronger chemical bond in oxybenzoate-oxybenzoate as compared to that in ethylene-terephthalate. Additionally, owing to the rigid-rod nature of the poly(oxybenzoate) segment, the frequency factor in the interchange reaction in poly(oxybenzoate) segment and polycarbonate is much higher than that in poly(ethylene terephthalate) segment and polycarbonate (i.e. 1036 versus 1014 min-1). Miscibility and the induced gamma->alpha crystal transformation in blends of random liquid crystalline copoly(oxybenzoate-ethylene terephthalate) at molar ratio 60/40 (P64) and polyamide 6 (PA6) were investigated with differential scanning calorimetry and wide-angle X-ray diffraction. It was found that P64 and PA6 were partially miscible at melt state as evidenced from the appearance of a single Tg and the Flory-Huggins interaction parameter being –0.18 through the melting point depression analysis. The presence of a small amount of P64 in PA6, around 5 %, induced additional crystallization of the alpha-form crystal in the quenched PA6. Moreover, the onset temperature for the gamma->alpha crystal transformation in the 5/95 P64/PA6 blend was reduced by 30 oC as compared to that in the pure PA6 case (160 oC vs. 130 oC). The kinetics of ester-amide exchange in blends of P64 and PA6 were studied with 13C nuclear magnetic resonance. It was found that the ester-amide interchange in the two polymers took place within 15 min when the blend was annealed at 260oC. The activation energies of ester-amide exchange in 30/70, 50/50 and 70/30 P64/PA6 blends were all about 24.0 kcal/mol. The pre-exponential factors for ester-amide exchange in 30/70, 50/50 and 70/30 P64/PA6 blends were 2.01×1011 min-1, 2.59×1010 min-1 and 2.74×1011 min-1, respectively, which is probably due to phase homogeneity as displayed by the micrographs from the polarized optical microscopy.
|Appears in Collections:||Thesis|